Sounds similar to sorting by zip code. I don’t know how many postmen share each zip code. In Copenhagen the western district has been sub-divided into a lot of

Sounds similar to sorting by zip code. I don’t know how many postmen share each zip code. In Copenhagen the western district has been sub-divided into a lot of zip codes so it could be that each is its own route, but they only did it for the western district, the other districts still only have a single zip code — I suspect that they did it to simplify sorting but found that people are more likely to make mistakes (when you have a dozen zip codes for the colloquially same district).